Bathroom Ventilation Rules Have Changed: What the Updated National Construction Code Means for Your

If you've dealt with a run of wet weather in recent years, you've probably also dealt with the fallout - foggy bathroom mirrors that never quite clear, a musty smell that won't shift, or worse, mould creeping into corners no matter how often you wipe it down. It's been a genuinely widespread problem across the country, and it's part of the reason the National Construction Code has recently been updated with clearer, stricter rules around residential ventilation.

If you're renovating, building, or just trying to figure out why your bathroom never seems to dry out properly, here's what's changed and what it means for you.

Why bathrooms are ground zero for mould

Mould needs three things to take hold: moisture, warmth, and still air. Bathrooms tick every box. Hot showers pump humidity into a small enclosed space, and if that moist air has nowhere to go, it settles into grout, ceilings, and cavity spaces where it lingers long after the room feels dry.

It's not just a cosmetic issue either. Beyond the damage mould does to building materials over time, airborne mould spores are a genuine health concern, linked to everything from mild respiratory irritation through to more serious infections in vulnerable people. Getting the airflow right isn't just about keeping the room looking fresh - it's a health and building-integrity issue.

What's actually changed in the Code

The updated National Construction Code takes direct aim at this problem through Part 10.8 of the Housing Provisions, which covers condensation management. A few of the key changes worth knowing:

• Exhaust air can no longer be dumped into the roof space. Air pulled from kitchens, bathrooms, sanitary compartments, and laundries now has to be ducted straight outside, rather than vented into the ceiling cavity where moisture used to quietly accumulate and cause exactly the kind of hidden damage the update is trying to prevent.
• Minimum flow rates are now specified. Bathrooms and sanitary compartments need a mechanical exhaust capable of at least 25L/s, while kitchens and laundries need at least 40L/s - a baseline that rules out underpowered fans that technically run but don't actually clear the air.
• Windowless bathrooms need a proper exhaust setup. If a bathroom or toilet doesn't have a window (or equivalent) for natural ventilation, it now needs a mechanical exhaust that either runs continuously, or is switched on with the light and includes a run-on timer that keeps it going for at least 10 minutes after the light's turned off - long enough to actually clear the humid air rather than cutting out the moment someone leaves the room.
• Fresh air still needs somewhere to come from. These rooms also need a source of fresh air, either through an opening to an adjacent space or in line with AS 1668.2.

The full technical detail sits with the Australian Building Codes Board if you want to read the Code itself.

What this means if you're renovating or building

For most homeowners, this comes down to one practical question: does your current bathroom exhaust actually meet the new flow rate and ducting requirements, or is it due for an upgrade? A lot of older exhaust fans were never rated to hit 25L/s in the first place, and plenty of homes still have fans venting straight into the roof cavity rather than outside.

If you're planning a bathroom renovation or a new build, it's worth checking your exhaust fan specs against the updated Code before you lock anything in. We carry a solid range of compliant exhaust fans suited to different bathroom sizes and duct configurations, along with exhaust fans with integrated lighting if you're after a combined fitting that saves a bit of ceiling space.

For bathrooms that also need heating in the cooler months, our bathroom heater range includes combination units that handle heating, lighting, and exhaust in one fitting - a genuinely practical option if you're trying to tick several boxes without cluttering the ceiling with separate units.

Getting it right the first time

Ventilation isn't the most exciting part of a bathroom renovation, but it's one of the parts you really don't want to get wrong - the cost of fixing mould and water damage down the track dwarfs the cost of installing the right exhaust fan now.

If you're not sure what flow rate or fan type your space needs, give our Thornton team a call. It's a straightforward conversation, and getting it sorted properly the first time will save you a much bigger headache later.